/Engine/Source/Editor/Persona/Public/IPersonaToolkit.h
Set the preview mesh, according to context (mesh, skeleton or animation etc.) Note that this sets the mesh in the asset and in the viewport (and may re-open the asset editor to apply this).
void SetPreviewMesh ( [USkeletalMesh](API\Runtime\Engine\Engine\USkeletalMesh) * InSkeletalMesh, bool bSetPreviewMeshInAsset )